1. Field of the Invention
Our invention pertains to hydraulic circuits for off-highway self-propelled work machines such as construction and industrial vehicles. More particularly our invention concerns an integrated hydraulic power circuit or system for work vehicles of the type comprising a hydraulic power steering system, a hydraulic torque converter, a hydraulic fluid-cooled retarder or brake system, and a hydraulic implement actuator or actuators.
2. Description of the Prior Art
The work vehicles of the type under consideration usually have two independent hydraulic circuits. One of these includes a power steering system, a brake cooling system, and an implement control system. The other incorporates a torque converter and transmission assembly. This known hydraulic power system consisting of two separate circuits has the following problems:
1. The power steering system wastes the incoming pressurized fluid, by directing same to a drain, when the steering control valve is not actuated.
2. The brake cooling system requires a constant supply of pressurized fluid from a large displacement pump or pumps, for proper cooling of the brake system.
3. The transmission lubricating circuit is fed from a single pump, which must therefore be also of sufficiently large displacement to feed the circuit by itself.
4. The two separate circuits of the power system demand their own oil coolers, one located dowstream of the brake cooling system and another located downstream of the torque converter.
5. The two separate circuits have respective filters, thereby increasing the cost and labor for maintenance.
6. The two separate circuits make the piping more complex and costly than does an integrated circuit.